Kai Ryssdal: There was a second explosion today at the damaged Fukushima nuclear reactor complex in Japan. A third reactor is in danger of overheating.

It goes without saying nuclear power companies around the world are watching nervously. Already today, Switzerland and Germany have canceled or suspended plans to build new plants. It all comes as public support for nuclear power had been growing. Yes, I said "had."

From the Marketplace Sustainability Desk, Scott Tong reports.

Scott Tong: Switzerland halted plans to build and replace nuclear plants. Germany today made a similar announcement. And the chairman of India's state-run nuclear company plans to "revisit the entire thing." Add it all up, and here's what it means, to industry consultant Alan Madian.

Alan Madian: 'Let's do a gut check and see what's going on here. And see whether we have to take radical action or whether we can get through this,' is what I'm hearing.

He's watching global public reaction. If it's strong, governments could pull critical subsidies to nuclear power. History says it could go either way.

Madian: Three Mile Island basically eliminated nuclear construction in the United States for three decades. On the other hand, Chernobyl did not slow the Russians down very much.

Madian says Russia is still a nuclear growth market, plus India, South Korea, and China, which is building 23 plants. The U.S. is building just five.

Harvard fellow William Tobey once ran the government's largest nuclear proliferation program. He expects regulators to reassess reactor risk. They need power for cooling. And Japan shows a single disaster can cut the first line of power -- the grid -- as well as the backup, diesel generators.

William Tobey: The lesson is, what may appear to be one-in-a-million odds, because they seem like independent probabilities, may not be.

It could bring new regulations. Several U.S. nuclear energy companies saw their stocks fall today. Domestically, more than 100 reactors crank out power now. But the White House wants subsidies for more, since nuclear is ultra-low carbon. And late this afternoon at the White House, regulators argued it's safe.

Gregory Jaczko chairs the Nuclear Regulatory Commission.

Gregory Jaczko: Bottom line right now we believe that the plants in this country continue to be designed to a very high standard for seismic and tsunami-type events.

Incidentally, at the Diablo Canyon plant in California, local officials asked for extra seismic studies for safety. They asked last March, almost a year to the day before this disaster.